Borg Warner T10 vs Toploader

[CompClassics]

Aluminum T10L cases were reproduced as were the T10M cases, I am not certain if they are still available. T10L and T10M gear sets can be found but as you stated can get expensive. That being said you can always use GM or other manufacturer gearsets, some have more desirable ratios than the Ford specific gear ratios and have a custom clutch disc made, most performance clutch manufacturers offer this service. Updated internal parts are available for the early T10 transmissions to help overcome their week points like popping out of gear (one of the biggest issues). These parts come from the Super T10 which became widely popular in the 70s and 80s for performance applications. You need to locate a Galaxie T10B iron case and tail shaft as this will provide the correct, transmission length, shifter position and mounting. The shifter assemblies can sometimes be an issue to find a rebuildable unit but you can use an aftermarket (Hurst) assembly also. Another issue the factory shifter unit has is the cross pin is smaller on the T10 shifters vs the Top Loaders shifter assembly which uses a larger diameter cross pin, I have swapped out the shifter boxes from the Top Loader to my T10, since Ford made both shifter assemblies they used the same mounting bolt patterns on both. You can put together a Ford Top Loader transmission assembly to bolt in place of a factory T10 transmission too if you desire. The T10 shifting is much smoother than the Top Loader in my opinion.
you might want to check out Richmound Gear, they bought the Borg Warner T10 design and still produce the transmission mostly for racing applications. There are other companies that also produce racing transmissions that utilize the T10 architecture and use such materials as magnesium for the cases. The B Production 289 Kirkham Cobra that we are currently putting together in our shop utilizes one of these hybrid T10 transmissions.